hi! hope I can help. I too purchased a goniopora foolishly without doing prior research. But I was lucky to have stumbled upon a website about this wonderful critter.
http://www.goniopora.org/ Unfortunately the site is either down or closed for good. I have had my "gonni" for over a year now and its doing great! On this website the author had done a series of experiments with feeding and had come up with a solution.
You must spot feed the coral. I use freezedried cyclopeeze and this has worked well for me, any small plankton type food will work as long as you get the coral fed.
-Feed once a week
-Use cyclopeeze or something similar, I just mix with a small amount of water
-Spot feed atleast a quarter of the mouths, I use an old syringe from a test kit
Its too bad the site is down it really help me out alot, infactmy coral is going to split soon in about 8 different directions.
Hope that helps
Cam